The present invention relates to an improvement in an electromagnetic pump of a type used for fuel supply in a vehicle.
A simple electromagnetic pump as a vehicle fuel supply pump which allows easy machining and assembly of parts and provides stable pumping has been desired. Conventional electromagnetic pumps have both advantages and disadvantages and fail to satisfy all the needs described above.
In a conventional electromagnetic pump of this type, as described in Japanese Utility Model Publication No. 57-20832, a sleeve member is fitted in a cylindrical housing having a U-shaped magnetic housing member, and a plunger is slidably fitted in the sleeve member. Inlet and outlet cylindrical members are mounted at two ends of the pump housing. This electromagnetic pump is called a rectangular type electromagnetic pump. In this conventional pump, a coil bobbin having an excitation coil thereon is loosely fitted in the sleeve member in the housing. Small-diameter cylindrical portions formed at inner ends of the inlet and outlet cylindrical members are fitted between the coil bobbin and the sleeve member. A magnetic flux path from the excitation coil is formed such that the plunger is reciprocally driven by the pump housing and the inlet and outlet cylindrical members in the sleeve. In particular, since the small-diameter portions properly constitute the magnetic flux path, the total magnetic efficiency can be improved to optimize pumping.
The conventional electromagnetic pump of the structure described above has a large number of constituting parts and a complicated structure. Machining and assembly are time-consuming and cumbersome. As a result, a compact, lightweight, low-cost electromagnetic pump cannot be provided.
With the above structure, as a member for forming the magnetic flux path necessary to achieve proper, smooth reciprocal movement of the plunger by means of the magnetic force from the excitation coil, the pump housing is machined as a U-shaped member by bending a relatively thick magnetic plate. Inner ends of the inlet and outlet cylindrical members are cut as the small-diameter portions. Manufacture of these parts is time-consuming and cumbersome, resulting in high cost. In addition, high precision cannot be assured. In a worst case, the sleeve member becomes deformed so that proper operation of the plunger cannot be guaranteed.
According to another conventional electromagnetic pump without the small-diameter portions of the inlet and outlet members, as described in Japanese Utility Model Publication No. 52-36964, a sleeve member has a plunger extending therethrough and is held by a coil bobbin. Thick magnetic plates (i.e., yokes) are arranged at two ends of the coil bobbin. With this structure, however, a magnetic plate as a magnetic flux path constituting member is required to increase a total number of constituting parts, the overall structure is complicated, and assembly is cumbersome. Since the magnetic plate is inserted between the coil bobbin and a printed circuit board, a projection is formed on a coil bobbin to insulate the printed circuit board from the magnetic plate when the coil is led from the coil bobbin to the printed circuit board. A thin insulating film such as a polyester or enamel film must be formed on the coil. Since such a film is very thin, electrical insulation between the coil and the magnetic plate and various electronic parts must be considered. The magnetic plate may be short-circuited with the electronic components, so that a wide space must be guaranteed therebetween. As described above, since the magnetic plate is relatively thick, a compact and lightweight pump cannot be prepared and the magnetic efficiency for driving the plunger is also degraded. As a result, efficient and accurate pumping cannot be obtained.
Electromagnetic pumps of this type have been mounted in small vehicles of 1,000 cc stroke volume, so that a demand has arisen for a compact, lightweight, low-cost pump. No conventional electromagnetic pumps can answer the above demand and much room is left for improvements. In reviewing the overall structure of the electromagnetic pump, demand has arisen for further improvements: simplification of the respective components, reduction in the number of parts so as to facilitate machining and assembly as well as an increase in operation reliability, thereby obtaining a compact, lightweight, low-cost electromagnetic pump.